PROSPECTUS SUPPLEMENT
 

Filed Pursuant to Rule 424(b)(3)
Registration No. 333-123677
Prospectus Supplement No. 1 dated July 1, 2005
(To Prospectus dated June 2, 2005)
NRG LOGO
NRG Energy, Inc.
420,000 Shares of 4% Convertible Perpetual Preferred Stock
10,500,000 Shares of Common Stock issuable upon conversion of the Preferred Stock
      This Prospectus Supplement supplements the prospectus dated June 2, 2005 (the “Prospectus”) of NRG Energy, Inc., relating to the sale by certain of our stockholders (including their pledgees, donees, assignees, transferees, successors and others who later hold any of the selling stockholders’ interests) of up to 420,000 shares of preferred stock, or 10,500,000 shares of our common stock issuable upon conversion of the preferred stock. You should read this Prospectus Supplement in conjunction with the Prospectus, and this Prospectus Supplement is qualified by reference to the Prospectus, except to the extent that the information in this Prospectus Supplement supersedes the information contained in the Prospectus.
      Investing in our preferred stock or common stock involves risks that are described in the “Risk Factors” section beginning on page 6 of the Prospectus.
      Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this Prospectus Supplement is truthful or complete. Any representation to the contrary is a criminal offense.
The date of this Prospectus Supplement is July 1, 2005


 

      The table of selling stockholders contained in the Prospectus is hereby superseded by the following table:
                                                         
    Ownership Before   Securities Offered by the   Ownership After Offering(2)
    Offering   Prospectus(1)    
                % of
Name   Preferred   Common(3)   Preferred   Common(3)   Preferred   Common   Common(4)
                             
AM International E MAC 63 Ltd. 
    790       19,750       790       19,750       0       0       0  
AM Master Fund I, LP
    6,916       172,900       6,916       172,900       0       0       0  
BBT Fund, LP
    6,750       168,750       6,750       168,750       0       0       0  
Boston Income Portfolio c/o Eaton Vance Mgt
    1,255       31,375       1,255       31,375       0       0       0  
Castlerigg Master Investments Ltd. 
    500       197,100       500       12,500       0       184,600       *  
Citigroup Global Markets Inc.(5)
    4,994       124,850       4,994       124,850       0       0       0  
City of New York Fire Dept Pension Fund High Yield
    200       5,000       200       5,000       0       0       0  
City of New York Police Pension Fund High Yield
    275       6,875       275       6,875       0       0       0  
City of New York Teachers Retirement System High Yield
    600       15,000       600       15,000       0       0       0  
CNH CA Master Account, LP
    5,500       137,500       5,500       137,500       0       0       0  
Coastal Convertibles Ltd. 
    1,500       37,500       1,500       37,500       0       0       0  
Concentrated Alpha Partners, LP
    6,750       168,750       6,750       168,750       0       0       0  
DBAG London
    11,000       275,000       11,000       275,000       0       0       0  
Delaware Dividend Income Fund, a series of Delaware Group Equity Funds V
    1,500       37,500       1,500       37,500       0       0       0  
Deutsche Bank Securities Inc. 
    2,552       63,800       2,552       63,800       0       0       0  
Diversified High Yield Bond Portfolio c/o Eaton Vance Mgt
    245       6,125       245       6,125       0       0       0  
Drawbridge Convertible I Ltd. 
    489       12,225       489       12,225       0       0       0  
Drawbridge Convertible II Ltd. 
    156       3,900       156       3,900       0       0       0  
Drawbridge Global Macro Masterfund Ltd. 
    3,310       82,750       3,310       82,750       0       0       0  
ELCA Unscreened — High Yield
    500       12,500       500       12,500       0       0       0  
Equitec Group, LLC
    500       12,500       500       12,500       0       0       0  
Fidelity Financial Trust: Fidelity Strategic Dividend & Income Fund(6)
    3,900       97,500       3,900       97,500       0       0       0  
Forest Fulcrum Fund LP
    1,573       39,325       1,573       39,325       0       0       0  
Forest Global Convertible Fund, Ltd., Class A-5
    2,860       71,500       2,860       71,500       0       0       0  
Forest Multi-Strategy-Maste r Fund SPC, on behalf of its Multi- Strategy Segregated Portfolio
    1,817       45,425       1,817       45,425       0       0       0  
Frontpoint Convertible Arbitrage Fund, LP
    8,000       200,000       8,000       200,000       0       0       0  
GLG Market Neutral Fund
    22,000       550,000       22,000       550,000       0       0       0  
Grace Convertible Arbitrage Fund, Ltd. 
    7,000       175,000       7,000       175,000       0       0       0  
Guggenheim Portfolio Company XXXI, LLC
    5,000       125,000       5,000       125,500       0       0       0  

2


 

                                                         
    Ownership Before   Securities Offered by the   Ownership After Offering(2)
    Offering   Prospectus(1)    
                % of
Name   Preferred   Common(3)   Preferred   Common(3)   Preferred   Common   Common(4)
                             
Hallmark Master Trust High Yield Fund c/o Eaton Vance Mgt
    70       1,750       70       1,750       0       0       0  
HFR CA Global Opportunity Master Trust
    1,484       37,100       1,484       37,100       0       0       0  
HFR CA Select Fund
    750       18,750       750       18,750       0       0       0  
HFR RVA Combined Master Trust
    525       13,125       525       13,125       0       0       0  
HFR RVA Select Performance Master Trust
    252       6,300       252       6,300       0       0       0  
High Income Portfolio c/o Eaton Vance Mgt
    865       21,625       865       21,625       0       0       0  
IAM National Pension Fund
    700       17,500       700       17,500       0       0       0  
Industriens Pensionsforsikring
    300       7,500       300       7,500       0       0       0  
ING T. Rowe Price Capital Appreciation Portfolio
    12,000       300,000       12,000       300,000       0       0       0  
Institutional Benchmarks Master Fund, Ltd. 
    1,500       37,500       1,500       37,500       0       0       0  
Int’l Union of Operating Engineers c/o Eaton Vance Mgt
    15       375       15       375       0       0       0  
JHVST MidCap Value B
    200       52,200       200       5,000       0       47,200       *  
JMG Capital Partners, LP
    2,350       58,750       2,350       58,750       0       0       0  
JMG Triton Offshore, Ltd. 
    2,850       71,250       2,850       71,250       0       0       0  
John Hancock Variable Series Trust I — Mid Cap Value Fund B
    200       48,600       200       5,000       0       43,600       *  
Kamunting Street Master Fund, Ltd. 
    23,500       587,500       23,500       587,500       0       0       0  
KBC Financial Products USA, Inc. 
    8,955       223,875       8,955       223,875       0       0       0  
KDC Convertible Arbitrage Fund LP
    3,000       75,000       3,000       75,000       0       0       0  
Laborers District Council & Contractors Pension FD of Ohio
    200       41,100       200       5,000       0       36,100       *  
LDG Limited
    130       3,250       130       3,250       0       0       0  
LIJ Invest — Global High Yield
    275       6,875       275       6,875       0       0       0  
Linden Capital LP
    1,628       40,700       1,628       40,700       0       0       0  
LLT Limited
    852       21,300       852       21,300       0       0       0  
Lyxor/ AM Investment Fund Ltd. 
    988       24,700       988       24,700       0       0       0  
Lyxor/ Forest Fund Limited
    3,622       90,550       3,622       90,550       0       0       0  
Lyxor/ Silverado Fund Ltd. 
    1,550       38,750       1,550       38,750       0       0       0  
McMahan Securities Co. LP
    45       1,125       45       1,125       0       0       0  
MSS Convertible Arbitrage 1
    20       500       20       500       0       0       0  
National Bank of Canada
    1,186       29,650       1,186       29,650       0       0       0  
Newport Alternative Income Fund
    2,972       74,300       2,972       74,300       0       0       0  
New York City Employees Retirement Systems Enhanced Yield
    700       17,500       700       17,500       0       0       0  
Pebble Limited Partnership
    2,490       62,250       2,490       62,250       0       0       0  

3


 

                                                         
    Ownership Before   Securities Offered by the   Ownership After Offering(2)
    Offering   Prospectus(1)    
                % of
Name   Preferred   Common(3)   Preferred   Common(3)   Preferred   Common   Common(4)
                             
Penn Series Flexibly Managed Fund
    5,600       140,000       5,600       140,000       0       0       0  
Penn Series-High Yield Bond Fund
    200       5,350       200       5,000       0       350       *  
Pensionsinvest — Global High Yield
    700       17,500       700       17,500       0       0       0  
PFA Invest — Global High Yield
    600       15,000       600       15,000       0       0       0  
RWDSU Local 338 High Yield Fund c/o Eaton Vance Mgt
    20       500       20       500       0       0       0  
S.A.C. Arbitrage Fund, LLC
    8,000       200,000       8,000       200,000       0       0       0  
Sage Capital Management, LLC
    3,000       75,000       3,000       75,000       0       0       0  
Salomon Brothers Asset Management, Inc.(7)
    6,700       167,500       6,700       167,500       0       0       0  
SEPTA High Yield Fund c/o Eaton Vance Mgt
    20       500       20       500       0       0       0  
Severn River Master Fund
    1,000       25,000       1,000       25,000       0       0       0  
Silverado Arbitrage Trading, Ltd. 
    500       12,500       500       12,500       0       0       0  
Silvercreek II Limited
    9,447       236,175       9,447       236,175       0       0       0  
Silvercreek Limited Partnership
    9,591       239,775       9,591       239,775       0       0       0  
Silver Point Capital Fund, LP
    1,365       1,042,333       1,365       34,125       0       1,008,208       1.2  
Silver Point Capital Offshore Fund, Ltd. 
    2,135       1,654,740       2,135       53,375       0       1,601,365       1.8  
SOCS Ltd. 
    10,000       250,000       8,000       200,000       2,000       50,000       *  
Sphinx Convertible Arbitrage SPC
    2,082       52,050       2,082       52,050       0       0       0  
Sphinx Fund
    140       3,500       140       3,500       0       0       0  
SRI Fund, L.P. 
    1,500       37,500       1,500       37,500       0       0       0  
Stanfield Offshore Leveraged Assets Ltd. 
    10,500       693,213       10,500       262,500       0       430,713       *  
Sunrise Partners Limited Partnership
    3,372       87,931       3,372       84,300       0       3,631       *  
The New America High Income Fund
    700       17,500       700       17,500       0       0       0  
TQA Master Fund, Ltd. 
    870       21,750       870       21,750       0       0       0  
TQA Master Plus Fund, Ltd. 
    1,510       37,750       1,510       37,750       0       0       0  
T. Rowe Price Capital Appreciation Fund
    33,600       840,000       33,600       840,000       0       0       0  
T. Rowe Price High Yield Fund
    7,550       203,400       7,550       188,750       0       14,650       *  
T. Rowe Price Mid-Cap Value Fund
    12,000       1,912,500       12,000       300,000       0       1,612,500       1.9  
TRP Institutional High Yield Fund
    975       26,600       975       24,375       0       2,225       *  
TRP Invest — Global High Yield
    1,700       42,500       1,700       42,500       0       0       0  
TRP SICAV Global High Yield Bond Fund
    1,800       47,775       1,800       45,000       0       2,775       *  
UBS AG London FBO HFS
    5,000       125,000       5,000       125,000       0       0       0  
UBS AG London FBO PFEL
    18,500       462,500       18,500       462,500       0       0       0  
UBS AG London FBO WBCP
    7,000       175,000       7,000       175,000       0       0       0  
UBS O’Connor LLC F/ B/ O O’Connor Global Convertible Arbitrage Master Ltd. 
    5,000       125,000       5,000       125,000       0       0       0  

4


 

                                                         
    Ownership Before   Securities Offered by the   Ownership After Offering(2)
    Offering   Prospectus(1)    
                % of
Name   Preferred   Common(3)   Preferred   Common(3)   Preferred   Common   Common(4)
                             
Volkswagen High Yield Bond Fund c/o Eaton Vance Mgt
    10       250       10       250       0       0       0  
Whitebox Convertible Arbitrage Partners, LP
    26,000       650,000       26,000       650,000       0       0       0  
Whitebox Diversified Convertible Arbitrage Partners, LP
    5,000       125,000       5,000       125,000       0       0       0  
Xavex Convertible Arbitrage 7 Fund
    150       3,750       150       3,750       0       0       0  
Zazove Convertible Arbitrage Fund, LP
    4,000       100,000       4,000       100,000       0       0       0  
Zazove Hedged Convertible Fund, LP
    2,000       50,000       2,000       50,000       0       0       0  
Zurich Institutional Benchmarks Master Fund Ltd. c/o TQA Investors, LLC
    180       4,500       180       4,500       0       0       0  
Zurich Institutional Benchmarks Master Fund Ltd. c/o Forest Investment Management LLC
    2,061       51,525       2,061       51,525       0       0       0  
 
* Less than 1%.
(1)  Amounts indicated may be in excess of the total amount registered due to sales or transfers exempt from the registration requirements of the Securities Act of 1933, as amended, since the date upon which the selling stockholders provided to us the information regarding their preferred stock.
 
(2)  The information regarding the beneficial ownership after resale of shares is based on the assumption that each selling stockholder will sell all of the shares of preferred stock and common stock owned by the selling stockholder and covered by the Prospectus.
 
(3)  Unless otherwise indicated, includes all shares of common stock issuable upon conversion of the preferred stock and assumes a conversion price of $40.00 per share, which is equal to an approximate conversion rate of 25 shares per share of preferred stock. However, this conversion price will be subject to adjustment as described under “Description of the Preferred Stock — Conversion Rights” in the Prospectus. As a result, the number of shares of common stock beneficially owned prior to this offering and the number of shares of common stock offered hereby may increase or decrease in the future.
 
(4)  Based on 87,047,034 shares of common stock outstanding as of June 30, 2005.
 
(5)  Citigroup Global Markets Inc. was a co-placement agent on the issuance of the preferred stock.
 
(6)  The entity is a registered investment fund advised by Fidelity Management & Research Company (“FMR Co.”), a registered investment adviser under the Investment Advisers Act of 1940, as amended. FMR Co., 82 Devonshire Street, Boston, Massachusetts 02190, a wholly-owned subsidiary of FMR Corp. and an investment adviser registered under Section 203 of the Investment Advisers Act of 1940, is the beneficial owner of 2,402,699 shares of our outstanding common stock as a result of acting as investment adviser to various investment companies registered under Section 8 of the Investment Company Act of 1940.
 
(7)  Salomon Brothers Asset Management, Inc. acts as discretionary investment advisor with respect to certain accounts that hold the preferred stock. Accordingly, Salomon Brothers Asset Management, Inc. may be deemed to be the beneficial owner of such preferred stock. Salomon Brothers Asset Management, Inc. is the beneficial owner and, therefore, the Selling Stockholder of the following accounts: General Motors Investment Corp. (5,000 shares), General Motors Broad Mandate (600 shares) and Smith Barney Convertible Fund (1,100 shares).

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